The problem is that I downloaded EasyRoads3D with a different version of Unity (IIRC 2022.2.something), and this somehow created a mismatch when importing it into a different version.

The solution was to remove the cached downloaded EasyRoads3D assets (Linux command shown):
```
$ rm -rf ~/.local/share/unity3d/Asset Store-5.x/AndaSoft
```
And then re-download it using the Unity version I want to use them in.

The cache location is found in [thos documentation](https://docs.unity3d.com/Manual/AssetStorePackages.html#asset-location).